Charge conduction process and photoelectrical properties of bulk heterojunction device based on sulphonated nickel phthalocyanine and rose Bengal

The dependence of photovoltaic performance of the bulk heterojunction photovoltaic device based on the blend of sulphonated nickel phthalocyanine (NiPcS) and rose Bengal (RB) on their composition, thermal annealing and oxygen exposure has been investigated. It is found that both electron and hole mobility in RB phase and NiPcS phase, respectively has been increased on thermal annealing. The power conversion efficiency of the device increases upon thermal annealing, attributed the balance charge transport. The power conversion efficiency of the device experiences a drastic increase upon oxygen exposure, which attributed to the photo-induced doping, increase in exciton diffusion length in NiPcS phase and increased volume of exciton dissociation interfacial sites. From the impedance spectroscopy, we conclude that the change in bulk resistance and dielectric constant of the active material due to the illumination has a direct relevance to the photocurrent generated by the device.     

电离层中性气体释放的早期试验效应研究

在电离层释放电子吸附类中性气体能够引起电离层电子密度耗空,在释放之后快速形成"电离层洞";同时,由于释放气体的快速膨胀,挤压背景等离子体,在电离层洞的外边缘产生"壳状"电子密度增强结构,电离层洞和电子密度增强结构同时存在是释放早期试验效应的显著特征.本文研究了电离层中性气体释放的早期试验效应,建立了释放早期电子密度的时空演化物理模型,仿真了释放早期电子密度的时空演化过程,同时采用射线追踪方法研究了释放后10 s和120 s不同频率信号在扰动区的传播效应,并反演得到了电离层垂直探测电离图,反演结果与一次火箭喷焰的实际观测结果吻合较好,初步验证了本模型的正确性.     

退火对AlGaInP/GaInP多量子阱 LED外延片性能的影响

采用LP-MOCVD技术在n-GaAs衬底上生长了AlGaInP/GaInP多量子阱红光LED外延片.研究表明退火对外延片性能有重要影响.与未退火样品相比,460℃退火15min,外延片p型GaP层的空穴浓度由5.6×10¹⁸cm^-3增大到6.5×10¹⁸cm^-3,p型AlGaInP层的空穴浓度由6.0×10¹⁷cm^-3增大到1.1×10¹⁸cm^-3.但退火温度为780℃时,p型GaP层和p型AlGaInP层的空穴浓度分别下降至8×10¹⁷cm^-3和1.7×10¹⁷cm^-3,且Mg原子在AlGaInP系材料中的扩散加剧,导致未掺杂AlGaInP/GaInP多量子阱呈现p型电导.在460～700℃退火范围内,并没有使AlGaInP/GaInP多量子阱的发光性能发生明显变化.但退火温度为780℃时,AlGaInP/GaInP多量子阱的发光强度是退火前的2倍.     

氧离子注入微晶金刚石薄膜的微结构与光电性能研究

本文系统研究了氧离子注入剂量和退火温度对含有Si-V发光中 心的微晶金刚石薄膜的微结构和光电性能的影响. 结果表明, 氧离子注入并在较高温度退火有利于提高薄膜中Si-V中心的发光强度. 当氧离子注入剂量从10¹⁴ cm^-2增加到10¹⁵ cm^-2时, 薄膜中Si-V发光强度增强. Hall效应测试结果表明退火后薄膜的面电阻率降低. 不同温度退火时, 氧离子注入薄膜的Si-V发光强度较强时, 薄膜的面电阻率增加, 说明Si-V发光中心不利于提高薄膜的导电性能. Raman光谱测试结果表明, 薄膜中缺陷数量的增多会增强Si-V的发光强度, 而降低薄膜的导电性能. 关键词： 金刚石薄膜 氧离子注入 电学性能 Si-V缺陷     

Photoluminescence and paramagnetic defects in silicon-implanted silicon dioxide layers

Thermally grown SiO₂ layers on Si substrates implanted with Si⁺ ions with a dose of 6×10¹⁶ cm⁻² were studied by the techniques of photoluminescence, electron paramagnetic resonance (EPR), and low-frequency Raman scattering. Distinct oxygen-vacancy associated defects in SiO₂ and non-bridging oxygen hole centers were identified by EPR. The luminescence intensity in the 620 nm range was found to correlate with the number of these defects. The low-frequency Raman scattering technique was used to estimate the average size of the Si nanocrystallites formed after the implantation and thermal annealing at T>1100°C, which are responsible for the photoluminescence band with a maximum at 740 nm. The intensity of this band can be significantly enhanced by an additional treatment of the samples in a low-temperature RF plasma.     

Effects of post-sinter annealing on microstructure and magnetic properties of Nd–Fe–B sintered magnets with Nd–Ga intergranular addition

We investigate the effects of post-sinter annealing on the microstructure and magnetic properties in B-lean Nd–Fe–B sintered magnets with different quantities of Nd–Ga intergranular additions. The magnet with fewer Nd–Ga additions can enhance 0.2 T in coercivity, with its remanences nearly unchanged after annealing. With the further increase of the Nd–Ga addition, the annealing process leads coercivity to increase 0.4 T, accompanied by a slight decrease of remanence. With the Nd–Ga addition further increasing and after annealing, however, the increase of coercivity is basically constant and the change of remanence is reduced. Microstructure observation indicates that the matrix grains are covered by continuous thin grain boundary phase in the magnets with an appropriate Nd–Ga concentration after the annealing process. However, the exceeding Nd–Ga addition brings out notable segregation of grain boundary phase, and prior formation of part RE6 Fe13 Ga phase in the sintered magnet. This prior formation results in a weaker change of remanence after the annealing process.Therefore, the diverse changes of magnetic properties with different Nd–Ga concentrations are based on the respective evolution of grain boundary after the annealing process.     

新型碳材料在钙钛矿太阳电池中的应用研究进展

新型碳材料如石墨烯及其氧化物、碳纳米管、富勒烯及石墨炔等因其优异的热学、力学、电学、光学性能成为了钙钛矿太阳电池研究的又一亮点. 本文总结了新型碳材料在钙钛矿太阳电池对电极、电子传输材料及空穴传输材料中的研究进展, 新型碳材料的引入有效地提高了钙钛矿电池的性能, 为下一步新型碳材料的应用开发以及钙钛矿电池器件的研究提供了新的思路.     

High field phenomena in thin plasma nitrided SiO2 films

The effects of high field tunnel electron injection on the electrical properties of Al - thin plasma nitrided SiO₂ films - Si (p-type) structures are studied. Under high field injection, it has been observed that electron trapping, positive charge generation near the Si-SiO₂ interface (slow states) and fast state generation at the Si-SiO₂ interface have taken place. After high temperature N₂ annealing, the nitridation induced electron trap density is considerably decreased. Furthermore, under high field injection the generation rate of both the slow states and the interface states and consequently, the degradation rate of the nitrided oxide films have been also decreased after annealing.     

退火温度对硼掺杂纳米金刚石薄膜微结构和p型导电性能的影响

采用热丝化学气相沉积法制备硼掺杂纳米金刚石 (BDND) 薄膜, 并对薄膜进行真空退火处理, 系统研究退火温度对BDND薄膜微结构和电学性能的影响. Hall效应测试结果表明掺B浓度为5000 ppm (NHB) 的样品的电阻率较掺B浓度为500 ppm (NLB) 的样品的低, 载流子浓度高, Hall迁移率下降. 1000 ℃退火后, NLB和NHB 样品的迁移率分别为53.3和39.3 cm²·V^-1·s^-1, 薄膜的迁移率较未退火样品提高, 电阻率降低. 高分辨透射电镜、紫外和可见光拉曼光谱测试结果表明, NLB样品的金刚石相含量较NHB样品高, 高的硼掺杂浓度使薄膜中的金刚石晶粒产生较大的晶格畸变. 经1000 ℃退火后, NLB和NHB薄膜中纳米金刚石相含量较未退火时增大, 说明薄膜中部分非晶碳转变为金刚石相, 为晶界上B扩散到纳米金刚石晶粒中提供了机会, 使得纳米金刚石晶粒中B浓度提高, 增强纳米金刚石晶粒的导电能力, 提高薄膜电学性能. 1000 ℃退火能够恢复纳米金刚石晶粒的晶格完整性, 减小由掺杂引起的内应力, 从而提高薄膜的电学性能. 可见光Raman光谱测试结果表明, 1000℃退火后, Raman谱图中反式聚乙炔 (TPA) 的1140 cm^-1峰消失, 此时薄膜电学性能较好, 说明TPA减少有利于提高薄膜的电学性能. 退火后金刚石相含量的增大、金刚石晶粒的完整性提高及TPA含量的大量减少有利于提高薄膜的电学性能. 关键词： 硼掺杂纳米金刚石薄膜 退火 微结构 电学性能     

Lowering the driving voltage and improving the luminance of blue fluorescent organic light-emitting devices by thermal annealing a hole injection layer of pentacene

We chose pentacene as a hole injection layer (HIL) to fabricate the high performance blue fluorescent organic light-emitting devices (OLEDs). We found that the carrier mobility of the pentacene thin films could be efficiently improved after a critical annealing at temperature 120 °C. Then we performed the tests of scanning electron microscopy, atomic force microscopy, and Kelvin probe to explore the effect of annealing on the pentacene films. The pentacene film exhibited a more crystalline form with better continuities and smoothness after annealing. The optimal device with 120 ℃ annealed pentacene film and n-doped electron transport layer (ETL) presents a low turn-on voltage of 2.6 V and a highest luminance of 134800 cd/m² at 12 V, which are reduced by 26% and improved by 50% compared with those of the control device.     

Photoemission cross section:A critical parameter in the impurity photovoltaic effect

A numerical study has been conducted to explore the role of photoemission cross sections in the impurity photovoltaic(IPV) effect for silicon solar cells doped with indium. The photovoltaic parameters(short-circuit current density, opencircuit voltage, and conversion efficiency) of the IPV solar cell were calculated as functions of variable electron and hole photoemission cross sections. The presented results show that the electron and hole photoemission cross sections play critical roles in the IPV effect. When the electron photoemission cross section is 10-20cm~2, the conversion efficiencyη of the IPV cell always has a negative gain(?η 0) if the IPV impurity is introduced. A large hole photoemission cross section can adversely impact IPV solar cell performance. The combination of a small hole photoemission cross section and a large electron photoemission cross section can achieve higher conversion efficiency for the IPV solar cell since a large electron photoemission cross section can enhance the necessary electron transition from the impurity level to the conduction band and a small hole photoemission cross section can reduce the needless sub-bandgap absorption. It is concluded that those impurities with small(large) hole photoemission cross section and large(small) electron photoemission cross section,whose energy levels are near the valence(or conduction) band edge, may be suitable for use in IPV solar cells. These results may help in judging whether or not an impurity is appropriate for use in IPV solar cells according to its electron and hole photoemission cross sections.     

Hydrogen neutralization of dopant in p-type Ga0.47In0.53As

Diffusion of hydrogen has been performed in a series of zinc doped GaInAs layers using a RF hydrogen plasma. In highly doped (≈10¹⁹/cm³) materials, the free hole concentration decrease is accompanied by a significant increase of the hole mobility indicating a neutralization process of acceptors. Layers doped at a level of ≈10¹⁸/cm³ turn to n-type after hydrogenation. We also show that the hydrogen solubility in this material is fixed by the free hole density rather than by the hydrogen plasma conditions.     

Amorphous SiC film formation on Si(100) using electron beam excitation

The effect of electron impact on methylsilane (CH₃SiH₃) conversion to amorphous-Si_0.5C_0.5:H (a-Si_0.5C_0.5:H) films on Si(100) has been studied by Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption (TPD), and low energy electron diffraction (LEED). It is found that electron impact greatly enhances CH₃SiH₃ decomposition on Si(100) at both 90 K and 300 K, resulting in a-Si_0.5C_0.5:H thin film formation. Thermal annealing of the film causes hydrogen desorption and amorphous silicon carbide (a-SiC) formation. Upon annealing to temperatures above 1200 K, the a-SiC film became covered by a thin silicon layer as indicated by AES studies. Ordered structures are not produced by annealing the a-SiC up to 1300 K.     

Excess Si concentration dependence of the photoluminescence of Si nanoclusters in SiO2 fabricated by ion implantation

A method for the fabrication of luminescent Si nanoclusters in an amorphous SiO₂ matrix by ion implantation and annealing, and the detailed mechanisms for the photoluminescence are reported. We have measured the implanted ion dose, annealing time and excitation energy dependence of the photoluminescence from implanted layers. The samples were fabricated by Si ion implantation into SiO₂ and subsequent high-temperature annealing. After annealing, a photoluminescence band below 1.7 eV has been observed. The peak energy of the photoluminescence is found to be independent of annealing time and excitation energy, while the intensity of the luminescence increases as the annealing time and excitation energy increase. Moreover, we found that the peak energy of the luminescence is strongly affected by the dose of implanted Si ions especially in the high dose range. These results indicate that the photons are absorbed by Si nanoclusters, for which the band-gap energy is modified by the quantum confinement effects, and the emission is not simply due to direct electron–hole recombination inside Si nanoclusters, but is related to defects probably at the interface between Si nanoclusters and SiO₂, for which the energy state is affected by Si cluster–cluster interactions. It seems that Si nanoclusters react via a thin oxide interface and the local concentrations of Si nanoclusters play an important role in the peak energy of the photoluminescence.     

First-principles hybrid functional study of the electronic structure and charge carrier mobility in perovskite CH_3NH_3SnI_3

We calculate the electronic properties and carrier mobility of perovskite CH_3NH_3SnI_3 as a solar cell absorber by using the hybrid functional method. The calculated result shows that the electron and hole mobilities have anisotropies with a large magnitude of 1.4 × 10~4cm~2·V~(-1)·s~(-1) along the y direction. In view of the huge difference between hole and electron mobilities, the perovskite CH3NH3 Sn I3can be considered as a p-type semiconductor. We also discover a relationship between the effective mass anisotropy and electronic occupation anisotropy. The above results can provide reliable guidance for its experimental applications in electronics and optoelectronics.     

Annealing effects on the properties of Ga2O3 thin films grown on sapphire by the metal organic chemical vapor deposition

We have prepared the gallium oxide (Ga₂O₃) thin films on sapphire substrates by the metal organic chemical vapor deposition (MOCVD) technique. We have compared the two films with and without the thermal annealing by using the X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and the photoluminescence (PL) spectra. Postdeposition annealing of amorphous Ga₂O₃ films was found to increase the degree of crystallization and the surface roughness. The PL emission intensities of bands in the blue–green and the ultraviolet regions increased by the thermal annealing.     

The effects of deep trap population on the thermoluminescence of Al2O3:C

The influence of deep traps on the 450 K thermoluminescence (TL) peak of Al₂O₃:C is studied. Depending upon the sample and on the degree of deep trap filling, features such as the TL width, area and height can vary considerably. These effects are interpreted to be due to: (a) sensitivity changes introduced by competition mechanisms involving deep electron and hole traps, and (b) the multiple component nature of the 450 K TL peak. The influence of the deep traps on the TL was studied using different excitation sources (beta irradiation or UV illumination), and step annealing procedures. Optical absorption measurements were used to monitor the concentration of F- and F⁺-centers. The data lead to the suggestion that the competing deep traps which become unstable at 800–875 K are hole traps, and that the competing deep traps which become unstable at 1100–1200 K are electron traps. Both the dose response of the TL signal and the TL sensitivity are shown to be influenced by sensitization and desensitization processes caused by the filling of deep electron and hole traps, respectively. Changes in the TL peak at low doses were also shown to be connected to the degree of filling of deep traps, emphasizing the influence of deep trap concentration and dose history of each sample in determining the TL properties of the material. Implications of these results for the optically stimulated luminescence properties are also discussed.     

第一性原理研究钨掺杂对锐钛矿物性的影响

在实验上, W掺杂量在0.02083–0.04167的范围内时, 有关掺杂体系的电导率影响的研究有两种相悖的结论. 为解决这个问题, 本文采用第一性原理平面波模守恒赝势方法, 首先构建了两种Ti_0.97917W_0.02083O₂ 和Ti_0.95833W_0.04167O₂ 超胞模型, 分别对这两种模型进行了几何结构优化、能带结构分布和态密度分布计算. 同时还计算了掺杂体系的电子浓度、有效质量、迁移率和电导率. 计算结果表明, 在电子自旋极化或电子非自旋极化的条件下, W掺杂浓度越大、掺杂体系的电子浓度越大、有效质量越小、迁移率越小、电导率越大、导电性能越强. 由电离能和Bohr半径分析进一步证实了Ti_0.95833W_0.04167O₂ 超胞的导电性能优于Ti_0.97917W_0.02083O₂ 超胞. 为了研究掺杂体系的结构稳定性和形成能, 又分别构建了Ti_0.96875W_0.03125O₂, Ti_0.9375W_0.0625O₂两种超胞模型, 几何结构优化后进行了计算, 结果表明, 在电子自旋极化或电子非自旋极化的条件下, 在W掺杂量为0.02083–0.04167的范围内, W掺杂浓度越大、掺杂体系的总能量越高、稳定性越差、 形成能越大、掺杂越困难. 将掺杂体系的晶格常数与纯的锐钛矿TiO₂相比较, 发现沿a轴方向的晶格常数变大、沿c轴方向的晶格常数变小、掺杂体系的体积变大, 计算结果与实验结果相符合. 在电子自旋极化的条件下, 掺杂体系形成了半金属化的室温铁磁性稀磁半导体.     

The origin of photoluminescence in Ge-implanted SiO2 layers

Ge ions were implanted at 100 keV with 3×10¹⁶ cm⁻² into a 300  nm thick SiO₂ layer on Si. Visible photoluminescence (PL) around 2.1 eV from an as-implanted sample is observed, and faded out by subsequent annealing at 900°C for 2 h. However, PL shows up again after annealing above 900°C at the same peak position. Compared with the as-implanted sample, significant increase of Ge–Ge bonds is measured in X-ray photoelectron spectroscopy, and the formation of Ge nanocrystals with a diameter of 5 nm are observed in transmission electron microscopy from the sample annealed at 1100°C. We conclude that the PL peak from the sample annealed above 900°C is caused by the quantum confinement effects from Ge nanocrystals, while the luminescence from the as-implanted sample is due to some radiative defects formed by Ge implantation.     

700℃退火下铝调制镍硅锗薄膜的外延生长机理

文章研究了在700℃退火下,铝插入层调制镍和硅锗合金反应形成单相镍硅锗化物的生长机理.透射电镜测试结果表明,镍硅锗薄膜和硅锗衬底基本达到赝晶生长;二次质谱仪和卢瑟福沟道背散射测试结果表明,在镍硅锗薄膜形成的过程中,铝原子大部分移动到镍硅锗薄膜的表面.研究结果表明,铝原子的存在延迟了镍和硅锗合金的反应,镍硅锗薄膜的热稳定性和均匀性都得到了提高.最后,基于上述实验结果给出了铝原子调制形成外延镍硅锗薄膜的生长机理.